1. Field of the Invention
The present invention relates to a motor driving circuit, and in particular to a motor driving circuit capable of outputting a dual frequency generator (FG) signal, which is capable of reducing working hours and facilitating the convenience in use with more higher efficiency and less cost.
2. Description of Prior Art
In order to prevent the temperature of a system in an electronic product from becoming too high to suffer damage, a heat-dissipating fan is usually mounted in this system. With this arrangement, when the temperature of the system exceeds a threshold value, the fan will be activated to reduce the temperature of the system for heat dissipation.
The above-mentioned heat-dissipating fan is activated by a motor. Generally, a brushless DC motor (referred to as “BLDC” hereinafter) is popular in the industry because of its easy maintenance, good controllability, and excellent performance. The BLDC can be applied in a wide range from a small motor inside a hard disk driver (or an optical disk driver) to a large motor for an electric vehicle because the BLDC can has advantages of high efficiency, stable rotating speed, large torque, durability and easy maintenance.
The conventional BLDC is controlled by an internal motor driving circuit, thereby controlling the rotating speed of the motor or the like. The motor driving circuit includes a control unit and a Hall component. The Hall component detects the phase change in a motor rotor to generate a Hall signal. The Hall signal is outputted to the control unit. Then, the control unit performs a logic operation to the Hall signal, thereby generating a control signal for controlling the operation of the motor.
The control unit further has a frequency generator output terminal for outputting a frequency generator (FG) signal. The FG signal is a signal having the same frequency as that of the Hall signal. The FG output terminal is connected to an external system (such as a computer), so that the external system can monitor the rotating speed of the motor based on the received FG signal.
However, a common four-pole BLDC merely outputs a FG signal to the external system based on Formula: F=2N/60. If a dual FG signal is to be obtained, an eight-pole BLDC has to be used, thereby outputting a dual FG signal to the external system based on Formula F=4N/60 (N represents the rotating speed of the fan). As a result, it is inconvenient to output a dual FG signal in practice.
However, in practice, the mold for manufacturing a four-pole BLDC is not compatible with the mold for manufacturing an eight-pole BLDC, so that it is necessary to provide an additional mold to manufacture an eight-pole BLDC, which increases the production time and cost.
According to the above, the conventional art has disadvantages of inconvenience, increased cost and working hours.
Therefore, it is an important issue for the present inventor and the manufacturers in this filed to solve the above-mentioned problems in prior art.